A crankshaft as employed in an engine that can be mounted, e. g., in an automobile has pins and journals typically milled and thereby machined, i. e., shaped, by a crankshaft miller in a workpiece.
A crankshaft shaping miller known in the art is described, e. g., in Japanese Unexamined Patent Publication No. Hei 6-297221.
A crankshaft miller as described in that publication makes use of a cutter which is smaller in width than a pin and a journal of a crankshaft to be machined, in order to permit a workpiece with pin and journal portions that vary in width to be machined by milling those portions each individually in a number of, say, six, divided steps.
The crankshaft miller to mill and thereby machine each of such pin and journal portions in a workpiece also requires the workpiece to be positioned with respect to an angle of rotation thereof, thus a phase position thereof.
Such phase positioning is effected by preliminarily machining a reference seat provided for this purpose in the one of counter weight portions that is located at one end of a workpiece and then, before the workpiece is introduced into the crankshaft miller and is clamped at its opposed ends each with a chuck, by bringing the phase positioning reference seat on the workpiece in contact with a phase positioning jaw located at one of the chucks.
The conventional crankshaft miller, however, makes it impossible to machine the one of journal portions that is located adjacent to the end of the workpiece at which the reference positioning seat is provided, because of interference between the cutter and the phase positioning jaw brought in contact with the reference seat.
This has hitherto required such a journal portion to be machined in a separate step using a separate machine tool such as a lathe. Poor productivity results from the increased number of machining steps necessitated and an added cost of the equipment is incurred because of the use of separate equipment such as a lathe thus rendering the prior art disadvantageous.
It is accordingly an object of the present invention to provide a method of machining a crankshaft from a workpiece whereby all of pin and journal portions of the workpiece are milled or thereby machined with a single crankshaft miller unit.